1. Field of the Invention
The present invention relates to a unit checking device for checking whether a unit detachably provided to a device body is new or old, such a unit, and an image forming apparatus.
2. Description of the Related Art
In an image forming apparatus such as a printer, a copier, a multi-functional device, or a facsimile machine, for easy maintenance, a mechanism with a member which is relatively easily deteriorated and a container for a color material are provided as detachable units. A user or a service person replaces units in a timely manner to keep the mechanism performance good and to replenish the color material which is a consumable item.
The image forming apparatus determines, when a unit is attached (mounted) thereto, whether the unit is a brand-new unit having never been attached before or an old unit (secondhand unit). If the unit is determined to be a new unit, then the image forming apparatus performs, for example, various adjustments depending on the performance of the new member. The image forming apparatus then applies processing to the attached unit determined to be “new” in such a manner that the attached unit is handled as an “old unit” from now on.
There has been a technology for using a fuse to determine whether a unit is new or old (Japanese Unexamined Patent Application Publication No. 6-51585). According to the publication, the fuse is provided to a unit. When the unit is attached to an image forming apparatus, one end of the fuse is connected to the power source of the main body of the image forming apparatus, and an electric potential of the other end of the fuse is detected. The potential of the other end is equal to a potential of the power source when a fuse blowout is not caused. In such a case, the image forming apparatus determines that the unit is new, and then, a high-current is supplied to the fuse to cause a fuse blowout.
Another technology has been proposed in which a zener diode rather than a fuse is provided to a unit (Japanese Unexamined Patent Application Publication No. 10-240068). According to the publication, a potential of a cathode is detected while a predetermined voltage is applied to the zener diode. The potential of the cathode is equal to a predetermined potential corresponding to a breakdown voltage in a case where the zener diode is not broken. In such a case, the image forming apparatus determines that the unit is new, and then, a high-current equal to or greater than a rated current is supplied to the zener diode to break the zener diode.
In the foregoing conventional technologies, supplying a current to cause a fuse blowout or to break the zener diode is processing based on which a determination that a unit is old can be made.
Where a fuse or a zener diode is used for determination as to whether a unit is new or old, supplying a high-current equal to or greater than several hundreds of milliamperes is required to cause a fuse blowout or to break the zener diode. Therefore, it is necessary to use a switching element having a current capacity equal to or greater than the high-current to turn ON/OFF energization. A switching element having a large current capacity is large compared to that having a small current capacity. This causes a problem that a space large enough to mount such a large switching element has to be provided on a circuit board. The problem makes it difficult to reduce a space for the device body (to downsize the device body) to which the unit is attached and to reduce the cost of the device body.
There is also another problem that the fuse and the zener diode by themselves are expensive compared to the other circuit components. This makes it difficult to reduce the cost of the unit.